1. Field of the Invention
The present invention relates to a cantilever structure having nano-sized holes and a method of preparing the same, and more particularly, to a porous multi-scale cantilever structure having nano-sized holes prepared using anodic oxidation and electro-polishing and a method of preparing the same.
2. Description of the Related Art
A Conventional system of electrically or optically detecting micro-particles is quartz crystal mass balance (QCM). However, a quartz single crystal of QCM is so fragile that QCM cannot be made to become small and thin and is not suitable for mass-production.
However, small-sized sensors based on a micro electro mechanical system (MEMS) in which electric and mechanical components are recently united to be microminiaturized draw people's attention since the sensors response quickly, have high sensitivity, and are suitable for mass-production.
The MEMS enables the microminiaturized products to be mass-produced at a low cost by applying a microelectronics fabrication in which processes such as deposition, etching, etc. are repeatedly performed. In addition, the MEMS uses a driving force such as coulombic force that is a force between charged particles, a magnetic force, a force by a thermal expansion difference, etc., and the microminiaturized products significantly reduce their power consumption because of their small size. Therefore, the importance of the MEMS is highlighted along with nanotechnique and system on chip (SOC) technique.
In recent days, to detect a physical phenomenon or a chemical reaction, many studies in developing sensors based on MEMS processed cantilevers have been conducted.
FIGS. 1A through 10 are flow charts illustrating a method of preparing such a conventional cantilever structure. First, in FIG. 1A, a sacrificial layer 2 is formed on a substrate 1, and then a pattern is formed on the sacrificial layer 2 using a mask. In FIG. 1B, a material to become a cantilever 3 is deposited on the sacrificial layer 2, and then a pattern of the material to become a cantilever 3 is formed using another mask. Subsequently, when the sacrificial layer 2 is removed, a conventional cantilever structure as in FIG. 1C is formed.
Sensors using a cantilever under study measure static deflection of the cantilever according to mass change, etc. by absorbing heat or gases using a light source such as laser. However, in the case of a conventional sensor using a light source such as laser, the sensor has to have a light source so that decreasing a size of the sensor is limited.
Besides the method of sensing by static deflection by laser, there is a method of sensing using a change in resonance frequency. Thundat, et al of Oak Ridge National Lab confirmed in Applied Physics Letters 80, 2219-2221 (2002) that a spring constant change by Na+ ion absorption on a surface of a micro cantilever due to resonance frequency measurement could be measured. In addition, researchers in IBM Swiss Zurich laboratory reported that the sensing method by resonance frequency measurement could be used for sensing a predetermined gas of air.
However, all the methods described above use a reaction on a surface of the cantilever. Therefore, in order to obtain high sensitivity even at low driving voltage, it is desired that the cantilever has a larger surface area. However, there was a limit on increasing a surface area in a cantilever structure having a constant size. In addition, there is a method of increasing a surface area of a cantilever structure by preparing nanoholes using a lithography method that uses electron beam (E-beam), scanning tunneling microscope (STM), etc. on a surface of the cantilever structure. However, when the method is used, a manufacturing cost is high, a manufacturing process is complicated, and productivity is very limited.